Hope this is of help - edited for clarity:
Rules of the Air Regulations 2007
SECTION 3 LOW FLYING RULE
Low flying prohibitions
(3) The low flying prohibitions are as follows:
(a) Failure of power unit
An aircraft shall not be flown below such height as would enable it to make an
emergency landing without causing danger to persons or property on the surface
in the event of a power unit failure.
(b) The 500 feet rule
Except with the written permission of the CAA, an aircraft shall not be flown
closer than 500 feet to any person, vessel, vehicle or structure.
(c) The 1,000 feet rule
Except with the written permission of the CAA, an aircraft flying over a congested
area of a city town or settlement shall not fly below a height of 1,000 feet above
the highest fixed obstacle within a horizontal radius of 600 metres of the aircraft.
(d) The land clear rule
An aircraft flying over a congested area of a city, town or settlement shall not fly
below such height as would permit the aircraft to land clear of the congested area
in the event of a power unit failure.
6 The exemptions from the low flying prohibitions are as follows:
(ii) Any aircraft shall be exempt from the 500 feet rule when landing and takingoff
in accordance with normal aviation practice or air-taxiing.